Papers by Keyword: Oxidation Behavior

Abstract: In this study, oxidation behavior of ZrB₂-MoSi₂-SiC composite was investigated in the hot-pressed 5-20 vol% SiC-containing ZrB₂-20 vol% MoSi₂-based composites which were exposed to dry air between 1100°C and 1500°C up to 10 hours. The effects of SiC additive on the oxidation behavior were assessed. Experimental results showed that the weight gain due to oxidation exposure in air increased with increasing exposure temperature and exposure time. Parabolic oxidation behavior was observed for all the compositions composites. On the other hand, the weight gain decreased with increasing amount of SiC added. The addition of SiC improved the oxidation resistance of the composites, and the improvement was enhanced with increasing amount of SiC added. In addition, X-ray diffraction was used to identify major crystalline phases present in both the as-received and the post-oxidized composites. The oxidized sample surface was characterized by scanning electron microscopy and energy-dispersive X-ray spectroscopy. The microstructure of the post-oxidized composites consisted of two characteristic regions: oxidized reactive region and unreactive bulk material region. Furthermore, the oxidized reactive region divided into an outermost dense silica-rich scale layer and oxidized reactive mixture layer. The improvement of the oxidation resistance due to the addition of SiC is associated with the presence of the thicker dense outermost scale layer which inhibited inward diffusion of oxygen through it.

Abstract: The objective of this research is to investigate the oxidation behavior of typical extra heavy oil from Xinjiang oil field. TGA/DSC data of both oil and oil sands were obtained. The results indicates that both heavy oil and its sands exhibited similar patterns which can be characterized as three distinctive regions: low temperature oxidation, fuel deposition and high temperature oxidation. Further investigation of oil quartz and man-made sand with different amount of montmorillonite show that the existence of sands and clays enhance the exothermic behavior of oxidation reactions in fuel deposition and high temperature oxidation regions.

Abstract: The present study aims to investigate the oxidation behavioue of pressuerless sintered SiC ceramic with the AlN-Y₂O₃ as sintering additives. Two main aspects are considered: The evaluation of oxidation kinetics in the temperature rang 1200°C-1400°C for short term test (30hr) and the degradation of the flexural strength after oxidation at temperature 1400°C for 100hr. The microstructure of surface oxidation layer of silicon carbide at high temperature is studied, and the effect of reactive product s on the high temperature oxidation resistance is also analyzed. The results showed that the oxidation began at temperature more than 1200°C, and the oxidation kinetics is obeyed parabolic rule. After long term oxidation, the fracture strength decreased greatly.Key words: oxidation behavior, liquid phase sintering, silicon carbide

Abstract: Kinetics and products of oxidation behavior of binary Co-10Al, Co-10Si and Co-10Cr alloys at 0.1Mpa oxygen at 973 and 1073K were analyzed and compared. The investigations show that CoO doesn't provide protective properties at high temperatures. Among the three alloy components, Co-10Cr has better oxidation resistance at 973K, while Co-10Al has at 1073K, and the causes are given. In addition, the schematic model of scale growth process is presented.

Abstract: The oxidation behavior of a stable-oxidative-poly-Si-Fe (SOPSF) coagulant prepared by water glass and H₂SO₄ solution in treating a synthetic humic acid (HA) water was probed, in compraison with that of poly-Si-Fe (PSF) and Polyferric aluminum (PFA). The results revealed that the oxidization of SOPSF and PSF was very stable during the whole coagulation process, and played a role during the whole process including quiescent settling stage. While PFA almost gave no oxidization even at higher dose of 0.322 mmol.L^-1. The oxidization rate of SOPSF was slower than that of SOPSF hydrolysis and destabilization process. Coagulation mechanism of SOPSF in removing dissolved organic matters (DOMs) may be a comprehensive results between the alternating interaction of oxidization/adsorption-destabilization/oxidization, bridging and sweeping.

Abstract: The feature, structure and composition of oxide films of a TP304H steel oxidized under 650°C and 25MPa water vapor for 1~50h were analyzed by SEM, EDS and XRD. The oxidizing dynamic curves were measured by discontinuous weighing method. The results indicated that the oxidation kinetics was agreement with the parabolic law. At the beginning of the oxidation, the formation of oxide was Fe2O3, while Fe3O4 and FeCr2O4 were formed with the increasing of oxidation time, without independent Cr2O3.

Abstract: Abstract: NiCoCrAlYSiHf coatings have been prepared by arc ion plating (AIP) on CrNi3MoVA steel ,which their microstructure and isothermal oxidation behavior at 950°C studied using SRD,SEM and EDAX. The results indicate that NiCoCrAlYSiHf coatings substantially increase the high-temperature oxidation resistance of CrNi3MoVA steel and the oxidation process was retarded mainly by the presence of α-Al2O3 oxide scale on the coating. Meanwhile, the major diffusion occured between the substrate element Fe and the coating element Co while Cr mainly distributed in the coating.

Abstract: The influence of oxidation behavior on super-plastic microforming of bulk metallic glass Zr₆₅Cu_17.5Ni₁₀Al_7.5 in the super-cooled liquid region was investigated. Samples were heated in air from room temperature to 395°C, 410°C, and 430°C, respectively, and kept under each temperature for 40 minutes. The increased weight of samples and the thickness of oxide layer were measured. Subsequently, the sample was compressed under 410°C with a micro gear silicon mold. In result, the oxide layer of the gear cracked and could be easily removed; also, the X-ray diffractometer showed that the gear core below the oxide layer remained an amorphous structure. It can be concluded that the oxidation behavior of Zr₆₅Cu_17.5Ni₁₀Al_7.5 does not affect the super-plastic deformation, which indicates the feasibility of super-plastic microforming process in air.

Abstract: The oxidation tests of the ZrB2-15vol.%SiC composite were carried out at 1673-1923 K under a low partial pressure of oxygen. Cross sections of the oxidized samples were studied using WDS. The reaction layer consists of ZrO2 and SiO2 at 1673 K. The SiO2 protective layer is formed on the surface. No apparent SiC depleted layer is observed. SiC depletion seems to occur at 1923 K and only the ZrO2 phase exists at the reaction layer. The passive oxidation occurs at 1673 K, whereas the active oxidation at 1923 K. The mass changes are quantitatively discussed by introducing a new emprical equation. The ZrB2-30 vol.%SiC composite is also discussed briefly.

Abstract: The spark plasma sintering (SPS) microstructure and high temperature oxidation behavior of TiH2-45Al-0.2Si-5Nb(at.%) alloy were investigated.Emphasis was placed on the effect of SPS microstructures, obtained by blend powder and mechanical alloying powder. The mass gain due to oxidation was measured using an electro balance. The oxide layers as well as its micro-structure were examined by SEM and EDS, and XRD. The results show that sintered microstructure of blend powder is composed of fully lamellar TiAl/ Ti3Al phase, and that of the mechanical alloying powder is composed of finer granular TiAl/Ti3Al phase. The latter oxidation rate is lower, and forms continuous mixed oxide layer of Al2O3 and TiO2. Both SPS microstructure of blend powder and mechanical alloying powder are superior in oxidation behavior to ordinary vacuum sintering.